/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.socket.server.upgrade;

import java.util.function.Supplier;

import reactor.core.publisher.Mono;
import reactor.netty.http.server.HttpServerResponse;

import org.springframework.core.io.buffer.NettyDataBufferFactory;
import org.springframework.http.server.reactive.AbstractServerHttpResponse;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.lang.Nullable;
import org.springframework.web.reactive.socket.HandshakeInfo;
import org.springframework.web.reactive.socket.WebSocketHandler;
import org.springframework.web.reactive.socket.adapter.NettyWebSocketSessionSupport;
import org.springframework.web.reactive.socket.adapter.ReactorNettyWebSocketSession;
import org.springframework.web.reactive.socket.server.RequestUpgradeStrategy;
import org.springframework.web.server.ServerWebExchange;

/**
 * A {@link RequestUpgradeStrategy} for use with Reactor Netty.
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 */
public class ReactorNettyRequestUpgradeStrategy implements RequestUpgradeStrategy {

    private int maxFramePayloadLength = NettyWebSocketSessionSupport.DEFAULT_FRAME_MAX_SIZE;


    /**
     * Configure the maximum allowable frame payload length. Setting this value
     * to your application's requirement may reduce denial of service attacks
     * using long data frames.
     * <p>Corresponds to the argument with the same name in the constructor of
     * {@link io.netty.handler.codec.http.websocketx.WebSocketServerHandshakerFactory
     * WebSocketServerHandshakerFactory} in Netty.
     * <p>By default set to 65536 (64K).
     *
     * @param maxFramePayloadLength the max length for frames.
     * @since 5.1
     */
    public void setMaxFramePayloadLength(Integer maxFramePayloadLength) {
        this.maxFramePayloadLength = maxFramePayloadLength;
    }

    /**
     * Return the configured max length for frames.
     *
     * @since 5.1
     */
    public int getMaxFramePayloadLength() {
        return this.maxFramePayloadLength;
    }


    @Override
    public Mono<Void> upgrade(ServerWebExchange exchange, WebSocketHandler handler,
                              @Nullable String subProtocol, Supplier<HandshakeInfo> handshakeInfoFactory) {

        ServerHttpResponse response = exchange.getResponse();
        HttpServerResponse reactorResponse = ((AbstractServerHttpResponse) response).getNativeResponse();
        HandshakeInfo handshakeInfo = handshakeInfoFactory.get();
        NettyDataBufferFactory bufferFactory = (NettyDataBufferFactory) response.bufferFactory();

        return reactorResponse.sendWebsocket(subProtocol, this.maxFramePayloadLength,
                (in, out) -> {
                    ReactorNettyWebSocketSession session =
                            new ReactorNettyWebSocketSession(
                                    in, out, handshakeInfo, bufferFactory, this.maxFramePayloadLength);
                    return handler.handle(session);
                });
    }

}
